This invention relates to 5-substituted-3-phenylimidazolidine-2,4-diones, to a process for their preparation and to their use in herbicidal formulations. In particular, this invention relates to 5-substituted-3-phenylimidazolidine-2,4-diones of the formula I ##STR2## in which:
X is hydrogen or halogen:
R is selected from the group --R.sup.2 or .dbd.CH--R.sup.3 ;
R.sup.1 is methyl or ethyl;
R.sup.2 is C.sub.1-8 alkyl. C.sub.3-8 haloalkyl, C.sub.3-8 cycloalkyl, C.sub.4-10 cycloalkylalkyl, phenyl, benzyl or substituted benzyl; and
R.sup.3 is C.sub.1-8 alkyl, C.sub.3-8 cycloalkyl, phenyl, substituted phenyl, benzyl, substituted benzyl, styryl, or a heterocyclic group of 3 to 10 ring atoms.
The compounds of the present invention, as will be seen from the description and test data which follow, have utility as both pre-emergence and post-emergence herbicides against a wide range of grassy and broadleaf plant species. The compounds are of particular interest when used against broadleaf plants.